MIPS 3.4.0 ABI and one-sized arrays

[Eric Botcazou <ebotcazou at act-europe dot fr>]

Hi,

The MIPS ABI fixes introduced a couple of problems for one-sized arrays in 
Ada on mips-sgi-irix6.5 (default ABI, n32 if I read correctly):
- the compiler ICEs on functions returning an one-sized array of floats 
(emit_move_insn between SImode and SFmode),
- one-sized arrays of integers are returned in the upper half of $2, while 
they were returned in the lower half previously.  If I read correctly again, 
this ABI change is not listed in http://gcc.gnu.org/gcc-3.4/mips-abi.html.

The keypoint is that such arrays are given the mode of their element by 
stor-layout.c, so they were previously handled like scalar values.  Now 
mips_return_in_msb catches them

/* Implement TARGET_RETURN_IN_MSB.  For n32 & n64, we should return
   a value in the most significant part of $2/$3 if:

      - the target is big-endian;

      - the value has a structure or union type (we generalize this to
	cover aggregates from other languages too); and

      - the structure is not returned in floating-point registers.  */

and we end up with the current unsatisfactory situation.


How should that be fixed?  A straightforward solution is to let 
mips_return_in_msb reject arrays with non-BLKmode, but this would mean 
changing the ABI for one-sized arrays of integers.

-- 
Eric Botcazou